Apparatus for fabricating wood structures

ABSTRACT

Hydraulic presses are disclosed which have relatively movable opposed platens for driving nailing plates into opposite sides of abutting wood members to form joints for wood roof trusses and the like. The presses are mounted on carriages supported for movement in substantially horizontal planes on stands or pedestals. During this inward and outward horizontal movement of the press between retracted and forward or operative positions, the presses are held against movement relative to the carriages, but in the forward or operative positions, when the platens are moved vertically toward and away from the opposite sides of the wood members, the presses are floatingly or resiliently supported on the carriages so as to avoid any substantial net upward or downward force being applied to the wood members during pressing of the plates into the wood. In one embodiment this is accomplished by employing a spring arrangement supporting the press, while in another embodiment a pneumatic system is employed for this purpose. Also described are such presses supported on pedestals which are made easily movable by an air lift system to different positions on a locating grid.

Moehlenpah et al.

3,720,950 Apr. 24, 1973 APPARATUS FOR FABRKCATHNG Primary Examiner-Billy J. Wilhite WOOD STRUCTURES Attorneyl(oenig, Senniger, Powers and Leavitt [75] Inventors: Walter G. Moehlenpah; David N.

Husman, both of St. Louis, Mo. [57] ABSTRACT 63110 Hydraulic presses are disclosed which have relatively Assigneez Hydro Air g g, Inc. St. movable opposed platens for driving nailing plates into Louis MO opposne sides of abuttmg wood members to form JOlIltS for wood roof trusses and the like. The presses [22] Filed: Jan. 8, 1968 are mounted on carriages supported for movement in substantial] horizontal lanes on stands or edestals. [21] Appl' 696323 During this inward and utward horizontal n iovement of the press between retracted and forward or opera- [52] US. Cl. .l00/100, 100/231, 100/264, tive positions, the presses are held against movement 100/269 R, 180/1 15, 227/152 relative to the carriages, but in the forward or opera- [51] Int. Cl. ..B30b 15/00 tive positions, when the platens are moved vertically [58] Field 01' Search ..227/152; 269/321 F; toward and away from the opposite sides of the wood 144/2886; 29/155; 100/226, 100, 229, 231, members, the presses are floatingly or resiliently sup- 264, 269; 180/1 15, 125 ported on the carriages so as to avoid any substantial net upward or downward force being applied to the [56] References Cited wood members during pressing of the plates into the wood. In one embodiment this is accomplished by em- UNITED STATES PATENTS ploying a spring arrangement supporting the press, 3,100,301 8/1963 Black ..227 152x While in another embodiment a PneumatiC System is 40 9 9 5 Bowman 227 152 employed for this purpose. Also described are such 3,253,665 5/1966 Schienle ..180/1 15 presses supported on pedestals which are made easily 3,358,348 12/ 9 MC nCh y-- --2 5 movable by an air lift system to different positions on 3,358,589 12/1967 Hentzschel ..lOO/231 X a l i id 3,388,657 6/1968 Jureit ..lOO/23 l X 36 Claims, 13 Drawing Figures 5/ /9 /5 U f 47 49 "Q 49 l 1v mmgmmemm 3.728.958

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APPARATUS FOR FABRHCATTNG WOOD STRUCTURES BACKGROUND OF THE INVENTION This invention relates to apparatus for fabricating wood structures, and more particularly to presses for fabricating wood roof trusses and the like.

Wood roof trusses are widely used in residential and commercial building construction. One such type of truss is a triangular truss consisting of a lower chord, upper chords joined to the ends of the lower chord at the heels of the truss and joined together at the peak of the truss, web members constituting compression members or struts extending from the third points of the lower chord to the midpoints of the upper chords, and web members constituting tension members or ties extending from the third points of the lower chord to the peak. This type of truss is commonly referred to as a W- truss. The lower chord may consist of two lengths of lumber positioned end-to-end and spliced together at the center of the length of the lower chord. Other well known types of trusses are the hip truss, the king-post and the scissors truss.

This invention is concerned with a press and apparatus including a plurality of presses for fabricating such trusses wherein nailing plates are driven into precut wood members to fasten them together, although it should be understood that the presses may be utilized for fabricating structures other than wood roof trusses, for example, for fabricating wall panel frames and floor trusses. There are several widely used systems for manufacturing wood roof trusses. One such system comprises a press suspended from an overhead carriage for movement to various locations for driving nailing or connector plates into assembled abutting precut wood truss members. Such a system is disclosed in the Moehlenpah et al. U.S. Pat. Nos. 3,068,484 and 3,069,684. In such apparatus, a press is suspended from one end of a beam counterbalanced by hydraulic apparatus for actuating the press mounted on the other end of the beam. The beam is pivotally suspended from a movable overhead carriage and thus the press is supported for universal movement to the various locations where nailing plates are to be forced into the wood members to form the truss joints. When this type of system is used for fabricating larger, heavier trusses using larger sizes of lumber, the press is suspended from the overhead carriage by a fluid chamber for preventing tilting or cocking of the press during the pressing operation. This system is disclosed in the Moehlenpah et al. U.S. Pat. No. 3,315,595. Although these systems are extremely efficient for producing trusses on a moderate production quantity basis, they are not adapted for high production output.

In another widely used system for fabricating wood roof trusses, a plurality of floor mounted presses are utilized. Such presses have one platen fixed on the base or pedestal and a head carrying the fluid operated cylinder and platen pivotally movable about a horizontal axis to permit the head and upper platen to be swung away from an opposing position between successive pressings thereby to facilitate loading of the precut wood members and unloading of the completed truss. This system is disclosed in the Moehlenpah et al. U.S. Pat. No. 3,068,483. Although this apparatus has also proven successful, provision must be made for permitting the precut and clamped wood members to move vertically during pressing. In addition, the pedestals of some of such presses are carried by either casters on rails or retractable casters on the floor for moving the presses to accommodate various types and sizes of trusses. The installation of the rails involves additional expense and repositioning of the presses can be time consuming.

There are also systems utilizing a plurality of presses which are movable horizontally between retracted positions for loading the wood members and unloading the completed trusses, and operative positions for the pressing operation. These presses are upwardly biased on their pedestals during both horizontal movement and pressing and must, therefore, be moved carefully and manually between their retracted and operative positions to avoid dislodging the nailing plates and damaging apparatus components during such movement. That is, with relatively soft and resilient spring supports, the presses must be moved to their operative positions slowly and carefully to avoid damage by collision of the platens with the wood members or other press structure. Thus, powered movement cannot be used. If relatively stiff and rigid spring supports are utilized, the presses during operation could apply substantial vertical forces to the wood members, thereby either lifting the wood members out of their clamps or causing the press to cock or rotate during pressing. Also, these presses are difficult and time consuming to move about when repositioning for fabricating other types or sizes of trusses.

Attempts have been made to solve the problem of weak truss joints caused by the application of vertical forces to the wood members during pressing. For example, in one of the prior art devices a motion divider, constituted by springs opposing closing movement of the platens, is provided for effecting simultaneous closing movement of the platens on the wood members. This causes the platens to simultaneously engage the opposite side of the wood members, thereby eliminating unequal vertical forces on these members. This system, however, neglects to take into consideration significant variations in wood thickness, straightness and homogeneity all of which are common in the wood members used for such trusses. Thus, notwithstanding the springs, if the wood members are not of uniform thickness, linearity and consistency, a net substantial vertical upward or downward force will be applied to the wood members during pressing and tight strong joints will not be formed.

SUMMARY OF THE INVENTION Among the several objects of this invention may be noted the provision of apparatus for fabricating wood roof trusses in which a press is horizontally movable on a carriage between a retracted and a forward or operative position for facilitating loading of the wood members and unloading of the completed trusses; the provision of such apparatus in which the press is held against movement relative to the carriage during horizontal carriage movement to maintain proper press alignment and to avoid striking fixed objects; the provision of such apparatus in which the press is floatingly or resiliently supported during closing movement of the press platens to accommodate for warpage and wood thickness and homogeneity variations, and for providing equal and cancelling forces on opposite sides of the wood members to substantially eliminate any significant net upward or downward forces thereon; and the provision of apparatus of the class described of high production capacity having easily positionable presses which can be readily installed and permit rapid changeover of truss type and size. In addition, the apparatus of this invention is characterized by simplicity of construction, low cost, and ease of operation and use.

Briefly, apparatus of this invention for fabricating trusses and the like at a work station at which nailing plates are to be driven into opposite sides of abutting wood members comprises a stand at the work station and a carriage mounted on the stand for movement between a retracted position away from the work station and a forward position at the work station. A fluid operated press having first and second opposed platens and fluid power means for moving the platens toward one another is provided. In addition, means are provided for supporting the press on the carriage in such manner that the press is held against movement relative to the carriage during movement of the carriage between its retracted and forward positions and is floatingly held on the carriage during closing movement of the platens. Other objects and features will be in part apparent and in part pointed out hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partial plan view of truss fabricating apparatus comprising press units of this invention at the junctures of the wood members of a wood W-truss;

FIG. 2 is a side elevation of one of the presses of FIG.

FIG. 3 is a front elevation of the press of FIG. 2;

FIG. 4 is a side elevation of the press of FIG. 2 in a moved position;

FIG. 5 is a rear elevation of the press of FIG. 2;

FIGS. 6-8 are enlarged vertical sections of a portion of the press of FIG. 2 in successive positions during a pressing operation;

FIG. 9 is a view similar to FIG. 4 of an alternate embodiment of the press; I

FIG. 10 is a view similar to FIG. 2 of the alternate press embodiment;

FIG. 11 is a view similar to FIG. 5 of the alternate press embodiment;

FIG. 12 is a pneumatic circuit diagram; and

FIG. 13 is a perspective of the alternate press em- DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to the drawings, FIG. 1 shows in apparatus arranged for assembling and nailing precut wood members to form a triangular or W roof truss T, such as shown in broken lines. As shown, truss T comprises a lower chord 1, upper chord members 3 which intersect at the peak of the truss, web members or struts 5 which extend between the third points on the lower chord to the mid-points on the upper chords, and web members or ties 7 which extend between the third points of the lower chord and the peak of the truss. At

the juncture of each of the upper and lower chord members with the struts and ties is a press, designated in its entirely at 9, for forcing nailing or connector plates N into the chords, struts and ties to splice them together. Similar presses are provided at the heels (not shown) of the truss. The presses 9 are carried by pedestals or stands 11, the latter being connected together in spaced relationship by means of adjustable booms 13, which may, for example, be of the type shown in the above-mentioned Moehlenpah et al. patents.

Referring to FIGS. 2-5, each of the stands 11 comprises a pair of vertically extending side frames 15 held in spaced parallel relationship by front and rear angle brackets 17. Each stand has casters 18 at opposite sides of its base riding on rails 19 fixed to the floor for movement of the stands to position the presses for forming various types of sizes of trusses. A screw hold-down knob 21 clamps the stand to the rails to hold it firmly in position during pressing. A U-shaped rail or track 23 is secured to the inside of each of the side frames 15 near the tops thereof with the open sides of the channels facing inwardly toward one another.

The press 9 is comprised of a generally C-shaped yoke or body portion 25 having an upper or first platen 27 rigid therewith. The bottom leg of the yoke 25 rigidly carries a first fluid power means, indicated generally at 29, constituted by a double-acting hydraulic cylinder 31 having a piston or ram (not shown) working in the cylinder. The ram carries a lower or second platen 33 at its upper end. Upper and lower hydraulic lines 35 and 37, respectively, are connected to the ends of hydraulic cylinder 31 for supplying hydraulic fluid under pressure to the cylinder for moving the platens toward and away from one another. A pair of rails 39 are secured to the tops of side frames 15. These rails carry adjustable angle brackets 41 for receiving the abutting ends of wood truss members T. Preferably, clamps (not shown) of the type shown in the above described Moehlenpah et al. U.S. Pat. Nos. 3,068,484 and 3,069,684 are provided for clamping the wood members relative to the stands. There is a vertically movable locator tray 43 spanning side frames 15 immediately above lower platen 33 on which a lower nailing plate N1 rests (FIG. 3). A similar nailing plate N2 is positioned above the intersection of truss members T.

Press 9, including press body 25, hydraulic power means 29, and upper and lower platens 27 and 33, is supported by means, including an assembly of springs generally indicated at 45, on a carriage 47 (FIGS. 1 and 13) of generally U-shape. The carriage has a pair of parallel legs 49, a cross-bar 51 and a plurality of casters 53 on legs 49 extending laterally for rolling engagement within the side frame tracks 23. Thus the press is supported on the carriage 47 which is movable horizontally on stand 11. A pair of angle arms 55 are welded to the opposite sides of hydraulic cylinder 31 and are interconnected to legs 49 of carriage 47 by assemblies 45, as will appear hereinafter.

A second fluid power means 57 for effecting horizontal inward and outward translatory movement of the press on the stand or pedestal is secured to the centers of front and rear cross-bars 17. This power means is constituted by a double-acting pneumatic cylinder 59 having first and second compressed air inlets 61 and 63, respectively, and a piston rod 65 extending from its rearward end. The piston rod 65 is adjustably secured to a depending arm 67 by a nut 69, the arm 67 being affixed at its upper end to carriage 47 at cross-bar 51. A pair of braces 71 interconnect the lower end of arm 67 and legs 49 of carriage 47. Thus, it will be seen that on actuation of cylinder 59, carriage 47 and press 9 will be moved horizontally on casters 53 between the forward or operative position shown in FIG. 2, for pressing nailing plates N1 and N2 into truss members T at a work station, and the retracted position shown in FIG. 4 away from the work station, for facilitating loading of the precut wood member and unloading of the completed truss.

Referring to FIG. 6, each of the assemblies 45 comprises upper or first and lower or second opposed coil compression springs 73 and 75, respectively, and a third preloaded flotation coil compression spring 77. A central rod 79 has a pair of nuts 81 at its upper end (the top one of which is welded to the bottom of lower platen 33) for movement of the rod with the platen. A pair of nuts 83 at the lower end of the rod carry a washer 84 supporting spring 75 at its lower end. The nuts 83 are threaded on rod 79 for constituting a means for vertically moving the center line upon which the platens close, as will appear, and rod 79 constitutes a means for interconnecting platen 33 with spring 75. The rod 79 is coaxially carried in a cylindrical tube 85 welded at its upper end to an elongate rocker plate 87 carried on the horizontal reach of carriage leg 49, with the tube 85 passing through a hole 86 in the leg. The lower end of tube 85 carries a washer 89 by means of a snap ring 91 for supporting the lower end of the flotation spring 77, the latter being coaxially coiled about tube 85 within spring 75. A washer 93 between springs 73 and 75 is slidably received on tube 85 and is carried by flotation spring 77 for supporting the lower end of spring 73. The bracket or arm 55, which is secured to hydraulic cylinder 31 of the press, is welded to a sleeve 95 slidably received on tube 85 at its upper end, the arm 55 and sleeve 95 thus constituting a means for interconnecting platen 27 and spring 73. The spring rates and diameters of springs 73 and 75 are substantially equal. The spring rate of spring 77 is minimal and its diameter is smaller than the diameter of springs 73 and 75. It will be seen that in the open or spaced-apart position of the press platens shown in FIGS. 2, 3, 4 and 6, lower platen 33 is bottomed or seated upon the upper end of cylinder 31. Thus, a portion of the weight of lower platen 33 (and the ram on which it is carried) is supported by cylinder 31. The remainder of the weight of the lower platen and the ram is directly supported on carriage 47 through engagement of nuts 81 with the upper ends of tubes 85, the latter being welded to plates 87 which are rockably carried by the carriage at legs 49. The carriage is supported on the stand for horizontal movement by engagement of casters 53 with rails 23. The remainder of the press weight, including upper platen 27, press body 25, cylinder 31 and that portion of the weight of the lower platen and ram seated on the upper end of cylinder 31, is also supported on the carriage, but is resiliently supported through springs 73 and 77. That is, the remainder of the press weight is supported through arm 55, upper spring 73, washer 93, flotation spring 77, tube 85, plate 87 and leg 49 of the carriage, the latter being carried by the stand through engagement of casters 53 with rails 23. Thus, when the platens are open, the entire press weight is carried by the carriage but is divided between direct support through nuts 81 and spring support through springs 73 and 77, with a majority of the weight being supported by the latter. Similarly, the weight of the lower platen and ram is divided between the direct and spring support. During closing movement of the platens, however, the weight of the entire press is supported through the spring support, as will appear hereinafter. Thus, as also will appear hereinafter, nuts 81 engaging the tops of tubes 85 constitute a means for firmly retaining the press on the carriage during horizontal movement of the carriage, and springs 77 constitute spring means for resiliently supporting the press on the carriage during closing movement of the platens.

Operation of the FIGS. 1-8 embodiment is as follows:

In the loading or unloading position of the press shown in FIG. 4, upper and lower platens 27 and 33 are open or spaced apart and the press body 25 is in its extreme left or retracted position. In this position, nailing plate N1 is placed in a predetermined position on locator tray 43 and precut wood truss members T are assembled and clamped in position on rails 39. Nailing plate N2 is then placed on top of the truss members at their intersection. The retracted position of press 9 facilitates loading of the precut truss members and nailing plates by providing an unobstructed loading area at the work station at the front of the press.

The pneumatic motor 57 is then actuated by means of a compressor (not shown) connected to line 61 to move the press horizontally to the right to its forward or operative position wherein upper and lower platens 27 and 33 are in vertical alignment with the truss members and nailing plates, as shown in FIG. 2. Thus, as motor 57 is actuated, piston rod moves toward the right as viewed in FIG. 4. This causes carriage 47, carrying the press, to move inwardly on casters 53 engaging tracks 23. It should be noted that motor 57 has conventional air cushioning at its ends for gradually decelerating the piston as it approaches the ends of its travel.

Hydraulic cylinder 31 is then actuated by supplying fluid under pressure to line 37 to advance platens 27 and 33 toward one another to press nailing plates N1 and N2 into the abutting ends of truss members T. When the nailing plates are fully driven into the truss members, fluid is supplied to line 35 to separate the platens and free the truss. Cylinder 59 is then actuated by supplying compressed air to line 63 to extend piston rod 65 and horizontally move the press from the FIG. 2

not lift the truss members out of their clamps or rotate the press. For example, if significantly more force is applied on the bottom of the joint than on the top, the truss members will lift out of their clamps and may deflect upwardly so that the joint assumes a V-shape with the bottom end edges abutting and the top end edges spaced apart. Similarly, if significantly more force is applied on the top of the joint than on the bottom, the press will rotate or cock about a horizontal axis and the platens will meet the nailing plates out of parallelism and will bend the teeth thereof. Accordingly, in order to insure a strong truss joint, it is necessary for the upper and lower platens to apply substantially equal forces on the opposite sides of the wood members, with the result that the press approximates weightlessness during pressing and the net vertical forces on the wood members do not become significant.

It is also important that the press be firmly held against movement relative to the carriage during translatory in and out movement of the carriage and press so that the platens do not strike the nailing plates, the locator tray or the wood members during such movement, and that it be held relatively floatingly or resiliently for substantial universal floating movement during opening and closing movement of the platens to accommodate for thickness variations, irregularities and warpage of the truss members. If the truss members are warped, for example, such that they are inclined at their ends in a downward direction from the rear of the press to the front of the press on rails 39, the press should be tiltable about a horizontal axis upon contact of the upper and lower platens with the nailing plates so that the platens assume the plane of the truss members. Thus, with the platens and truss members in parallel planes during the pressing operation, the nailing plates will be uniformly driven into the truss members to provide a strong joint. Similarly, if the wood is of improper thickness or if one side of the wood is harder than the other side, e.g., if a knot is present on only one side of the wood, the resilient support will permit the press to move vertically to maintain substantially equal and opposite pressing forces on the wood while driving in the nailing plates.

During horizontal inward and outward movement of the press and carriage on the stand, platens 27 and 33 are open or fully spaced apart with lower platen 33 being seated on the top of cylinder 31. As shown in FIG. 6, the weight of the lower platen and ram is divided between engagement of nuts 81 with the top of tube 85 and engagement of the bottom of the platen with the upper end of the cylinder. This latter portion of the weight of the lower platen and ram, together with the weight of upper platen 27, press body 25 and cylinder 31, is supported on the carriage through springs 73 and 77 as set forth above. The press is held firmly against movement relative to the carriage in this open condition of the platens because of this distribution of press components and lower platen weight. That is, it would require a force in excess of the total weight supported by direct engagement of nuts 81 with tube 85 to lift the press vertically when the platens are open. Similarly, it would require a force in excess of that portion of the weight of the lower platen and ram carried by engagement of lower platen 33 with cylinder 31 to lower the top platen when the platens are open. Since forces of these magnitudes are not exerted on the press when the platens are open, the press is held against movement relative to the carriage during horizontal movement of the carriagenThe press is therefore firmly retained on the carriage during movement of the carriage because a portion of the press weight is supported directly on carriage leg 49 via nuts 81 and plate 87. This support of the press on the carriage, including the elongate plates 87, wherein the press is held against upand-down vertical movement and front-to-rear rocking movement, insures that the platens are maintained in proper alignment during horizontal movement so that, for example, lower platen 33 does not strike locator tray 43 during its inward or outward travel.

When the press has completed its inward travel, hydraulic fluid under pressure is supplied to line 37 to advance the platens toward one another. The pressurized fluid acts in all directions below the piston in cylinder 31 and produces equal and opposite forces tending to move the piston and lower platen upwardly and the cylinder and upper platen downwardly. Since it requires less force for upper platen 27 to move downwardly compressing springs 73 and 77 than it does to raise lower platen 33 off of tubes 85, upper platen 27 initially moves downwardly until the forces are equalized, i.e., until the weight of lower platen 33 is supported by springs 73 and 77. The lower platen remains stationary during this initial movement. The position of assemblies 45 with the press in this initial moved position, hereinafter referred to as the poised position, is shown in FIG. 7.

After the upper platen has initially moved downwardly, the upper and lower platens simultaneously begin to advance toward one another at equal rates. As shown in FIG. 8, as the upper platen begins to move downwardly, arm compresses upper spring 73 against the upper surface of floating washer 93. Similarly, as lower platen 33 moves upwardly, washer 84 compresses lower spring 75 against the lower sur face of floating washer 93. Thus, the springs 73 and 75 interconnect and resist closing movement of the platens to insure equal approach rates of the platens toward the center line of the wood members. That is, since both platens are movable and since the hydraulic power means exerts equal and opposite forces against the bottom face of the piston and the bottom of the hydraulic cylinder during closing movement of the platens, the platens are prevented from moving at unequal rates because of the action of springs 73 and 75 about washer 93, the latter supporting the press through spring 77 and tube 85. It should be noted that in lieu of springs 73 and 75, which constitute compression means, a single spring may be used with a member fixed at its center for supporting engagement by spring 77 As soon as the lower platen begins to move upwardly and nuts 81 lift off of the top of tubes 85, the full weight of the press is supported on the stand (via the carriage) through springs '73, flotation springs 77, and tubes 85. As set forth above, the spring rate and preload of flotation springs 77 are such as to provide a relatively resilient or floating support for the press. Thus, in all positions of movement during closing of the platens, the entire press is held relatively floatingly on the carriage by springs 77 reacting between the point of abutment (washer 93) of springs 73 and 75 and the stand. This permits the press to rock or swing from side to side upon contact of the platens with a longitudinally warped or otherwise irregularly configured wood member and front to back upon contact of the platen with atransversely warped or otherwise irregularly configured wood member. Side-to-side rocking is accomplished through greater compression of one of springs 77 than the other while front-to-back rocking is accomplished through rocking of plates 87 on carriage legs 49. Springs 77 also permit the press to move vertically, as will appear.

When the upper platen engages nailing plate N2 and the lower platen lifts nailing plate N1 into engagement with the lower face of the wood members, the forces exerted by the platens on the opposite sides of the wood members are substantially equal. Hence, these forces substantially cancel each other, resulting in a net zero vertical force being applied to the wood members. In other words, the press is substantially weightless on the wood members during pressing. This insures that the wood members will be held flat in their clamps and the platens will be maintained parallel to the wood members.

Since substantially equal forces are exerted on the nailing plates, they will normally be driven into the opposite sides of the wood members at substantially equal rates. However, if one side of the wood is harder than the other, e.g., if the wood has a knot on one side, the platen on the harder side of the wood will remain stationary (or move slowly) while the platen on the softer side of the wood drives in the nailing plate. The force required to drive the nailing plate into the softer side of the wood progressively increases as the nailing plate is driven deeper into the wood. When this force increases until it is equal to the force necessary to drive the other nailing plate into the harder side of the wood, both platens advance and the nailing plates are fully driven into the wood. Therefore, even if one side of the wood is harder than the other side, the pressing forces exerted by the platens will remain substantially equal on opposite sides of the wood members. The resiliency of springs 77 permits the press and upper platen to move downwardly in this manner when the knot is on the lower side of the Wood members. The platens will similarly move if the wood is not of uniform thickness.

The horizontal center line upon which the press platens close may be lowered or raised by respectively threading nuts 83 up or down on rods 79. Forexample, if nuts 83 are threaded down rods 79, the vertical gap between the lower face of washer 93 and the upper end of spring 75 will increase. Thus, when the upper platen drops to the FIG. 7 poised position, washer 93 will not contact spring 75. Hence the lower platen will move upwardly and the upper platen will remain stationary until spring 75 is brought up into contact with washer 93, whereupon both platens then move toward each other on a vertically raised center line. Opposite movement of the nuts 83 will of course adjust the apparatus so the center line of platen closing is lowered.

In the embodiment of the invention illustrated in FIGS. 9-13, assemblies 45 are replaced with a pneumatic support, generally indicated at 101, which accomplishes substantially the same desirable results.

That is, the pneumatic support 101 holds the press against movement relative to the carriage during translatory movement between its retracted and forward or operative positions, and floatingly supports the press on the carriage during closing movement of the platens. Thus, the alignment of the press is maintained during translatory movement to avoid damage to the press by collision, for example, of the lower platen with the locator tray, and no net substantial vertical forces are applied to the wood members during pressing.

As illustrated in FIGS. 9-11 and 13, pneumatic support 101 constitutes a means for supporting the press on the carriage and comprises an expansible chamber or pneumatic actuator 103 having a housing 105 and an internal diaphragm 107 (FIG. 11). The diaphragm has a rod 109 secured to its center, the rod extending upward through a hole in the top of housing 105. A clevis 11 1 is provided at the upper end of the rod for pivotal attachment to a tongue 113 depending from press body 25. Actuator housing 105 is carried by the stand by a transverse bracket 115 and a pair of rods 117 on opposite sides of the press. Bracket 115 (FIG. 11) is bolted to the top of the housing at 119 and has side flanges 121 secured to the lower ends of rods 117. These rods extend upward through tubular guides 123 of arms or angle brackets 125, the latter being welded to the opposite sides of press body 25, and through holes in legs 49 of carriage 47. Flat rocker plates 127 are secured to the tops of rods 117 to suspend them from legs 49. Thus, press body 25 is supported on and interconnected to carriage 47 by rod 109, air actuator 103, bracket 115, rods 117 and plates 127 on carriage legs 49, the latter having casters 53 riding in tracks 23 on the stand. The heads of bolts 128 (FIG. 11) project upwardly from brackets for contact with legs 49 to limit upward movement of the press and to prevent frontto-rear rocking when the platens are open. These bolts are threaded in apertures in brackets 125 for vertical adjustment.

A compressed air supply, constituting a means for supplying air under pressure to actuator 103, is provided. This supply may be the same as that used for actuating horizontal movement cylinder 59, and will be described hereinafter. Actuator 103 is supplied with compressed air by a line 129 and is exhausted (at least partially) by a line 131 via a control valve 133, the latter constituting a means for reducing the pressure in the actuator. This valve is biased to a normally closed position but is actuable to open and reduce the pressure in actuator 103 by means of a depending arm 135 secured at 136 at its upper end to the rear edge oflower platen 33. The lower end of arm 135 has an adjustable bolt 137 with a compression spring 139 coiled thereabout. The head of bolt 137 engages valve 133 at button 141. When lower platen 33 moves upwardly upon actuation of hydraulic cylinder 31, arm 135 moves with it and releases button 141. This opensvalve 133 and reduces the pressure in actuator 103 to permit the press body and upper platen 27 to move downwardly, as will appear.

The pneumatic circuit for operating horizontal movement cylinder 59 and actuator 103 is illustrated in FIG. 12 as comprising a source of compressed air constituted by a fluid pump or air compressor 143 selectively connectible to either a line 145 or a line 147 through a two position control valve 149. This valve is biased by a spring 151 to the FIG. 12 position wherein compressor 143 is normally in communication with line 145 to extend piston rod 65 and hold the press in its retracted position, and to pressurize housing 105 of actuator 103 below diaphragm 107 to hold the press and the upper platen upwardly against vertical movement. Line 145 is in communication with the right-hand end of cylinder 59 via an adjustable restrictor 153 and a shunt-connected check valve 155, and with actuator 103 via a check valve 157.

When valve 149 is actuated by depressing a button 159 thereon, the compressor is connected to line 147 to retract piston rod 65 and move the press horizontally to its forward or operative position for the pressing operation. Line 147 is in communication with the lefthand end of cylinder 59 via an adjustable restrictor 160 and a shunt-connected check valve 161, and line 145 exhausts to atmosphere. As set forth above, valve 133 is actuated to reduce the pressure in actuator 103 by release of button 141 in response to initial upward movement of the lower p1aten.'This valve is connected to line 145 for venting line 131 to atmosphere through a spring biased pressure relief check valve 163.

As noted above, the stands or pedestals of the spring embodiment of the presses are mounted on casters 18 riding on rails 19 for movement of the presses to different positions for pressing different types and sizes of trusses. In the pneumatic embodiment of the press, an air cushion support, constituting a means for moving and locating at least some of the stands, is provided for the same purpose, although it should be understood that either support may be used with either of the presses. This stand is illustrated in FIGS. 9-11 and 13 as comprising a dome-shaped chamber 165 at the lower end of the stand between side frames 15 and a front and rear apron 167. The chamber 165 is formed by an arcuate metal plate 168 having an air passage 169 extending vertically through the top of the plate in communication with the chamber, the passage constituting a means for supplying the chamber with air under pressure. This passage is either connected to a high volume, low pressure blower (not shown) incorporated in each of the movable stands between the press and the chamber or to a valve or fitting adapted to be connected to a common blower for all of the movable stands. The movable presses are .held against movement after positioning by means of a vacuum holddown 170 within chamber 165, the hold-down being constituted by a rubber suction cup 171 and a metal back plate 172. Rods 173 extend upwardly from the backing plate 172 through a plate 174 fixed to the stand. Compression springs 175 are coiled about the upper ends of rods 173 between plate 174 and the heads of the rods. A vacuum line 176 communicates with the interior of the suction cup and is adapted to be connected to a vacuum pump (not shown) for drawing a vacuum in the suction cup to hold the press stationary on the floor. Rods 173 and springs 175 permit backing plate 172 to move downwardly when a vacuum is drawn in the suction cup. It should be noted that plate 168 is suitably sealed where rods 173 and line 176 pass through it. Alternatively, or in addition to the suction cup, the press may be weighted above the chamber by a heavy material 177, such as concrete, or electromagnets may be used if the base or floor upon which the press is carried is formed of a suitable magnetic material. As shown in FIGv 13, the base is marked with a locating grid 178 constituted by intersecting mutually perpendicular lines 179 and 181. The grid may either be painted directly on the floor of the building where the trusses are to be fabricated, or suitably etched or otherwise marked on a member such as a plastic sheet interposed between the floor and the presses.

Operation of the FIGS. 9-13 embodiment is as follows:

In the FIG. 9 loading position of the press, upper and lower platens 27 and 33 are fully open and the press body 25 is in its retracted position. Precut wood members T are clamped in position on rails 39 and nailing plates N1 and N2 are placed in position at the intersection of the wood members. The retracted position of the press facilitates this loading operation.

Pneumatic motor 57 is then actuated to move the press horizontally to the right to its forward or operative position wherein the upper and lower platens are in alignment with the wood members and the nailing plates, as shown in FIG. 10. To actuate motor 57 to move the press, button 159 of control valve 149 (FIG. 12) is depressed against the bias of spring 151. This connects compressor 143 to line 147 and to the lefthand end of cylinder 59 via check valve 161, and causes the piston and piston rod in cylinder 59 to move to the right. The right-hand end of the cylinder is exhausted to atmosphere through restrictor 153 and line 145. It should benoted that as motor 57 is actuated to move the press horizontally, the air in actuator 103 is trapped by valves 157 and 133 which is biased downwardly at this time by arm 135. Therefore the press body is rigidly held against movement relative to the carriage during this horizontal movement. Thus, the press can be moved rapidly without dislodging the nailing plates or damaging apparatus components by collision of the movable parts with the fixed parts, as could occur if the press were softly or floatingly supported during horizontal movement.

Hydraulic cylinder 31 is then actuated by supplying fluid under pressure to line 37 to advance platens 27 and 33 toward each other to press the nailing plates into the abutting ends of the truss members, as shown in FIG. 11. During the initial operation of hydraulic cylinder 31, the press body and upper platen 27 are held against downward vertical movement by air actuator 103. However, when lower platen 33 moves vertically upward, arm moves with it thereby releasing button 141 of valve 133 and establishing communication between lines 131 and through valve 163. Since line 145 is open to atmosphere, the magnitude of the pressure in actuator 103 is reduced to a value determined by the bias of the spring in valve 163. This reduced pressure is such that the press body and upper platen are permitted to move vertically downward. For example, for a press having a weight of approximately 300 lbs. and an actuator diaphragm area of approximately 9 in. sq., the initial pressure may be in the order of 60 psi to provide 540 lbs. of lifting force to firmly support the press against movement on the carriage.

When valve 133 is opened the pressure may be reduced to approximately 30 psi to reduce the lifting force to 270 lbs. and permit the press (300 lbs.) to move downwardly. Thus, valve 163 reduces the pressure in the air actuator by approximately 30 psi.

The reduced pressure (30 psi) in pneumatic actuator 103 provides a relatively soft or floating support for the press during closing movement of the platens. That is, the relatively low pressure on diaphragm 107 permits the diaphragm to flex in housing 105 in response to unequal resistance to movement of the upper and lower platens. For example, if the upper nailing plate N2 strikes a hard spot in the wood members (such as a knot), the upper platen will remain stationary (or more slowly) while the lower platen moves upwardly to drive in lower nailing plate N1 until the forces required to drive both nailing plates are equal. At that time both platens than advance until the nailing plates are fully driven into the wood members. If plate N1 strikes a knot on the lower side of the wood, the lower platen will remain stationary (or move slowly) until the upper platen and nailing plate have moved downwardly sufficiently to equalize the force necessary to drive in both plates. This downward vertical movement of the upper platen and press is possible because of the flexible support provided by the air actuator at reduced pressure between the carriage and the press. Thus, vertical forces on the wood members, caused by one of the nail ing plates requiring a greater force to penetrate a knot, for example, are substantially eliminated, resulting in a flat and strongjoint.

Vertical forces on the wood members are also minimized in the event that one of the platens contacts the wood members before the other. Thus, if the wood members are of improper thickness and one of the platens contacts them before the other, the first platen can only apply a force on the wood members equal to the difference in the press weight and the lifting force provided by the air actuator (i.e., 30 lbs. in the above example) before the second platen will be moved into contact with the wood members. Additionally, if the wood members are warped or tilted on the stand, the entire press, including both platens, will rock about a horizontal axis on plates 127 suspending the press from carriage legs 49 to assume the plane of the inclined or warped wood members and apply uniform pressing forces on the nailing plates.

To move one ormore of the presses to position them for fabricating other types or sizes of trusses, a compressed air supply of suitable velocity and volume is supplied to chambers 165 by either a common blower or individual blowers in each movable press. This produces a cushion of air under the stands and raises them slightly to enable easy horizontal movement across the floor. The grid 178 permits accurate placement and the concrete 177 and/or suction cup 170 (connected to a vacuum pump) eliminates the need for mechanical clamping or locking devices to hold the presses fixed on the floor. Thus, the expense and inconvenience of floor tracks and rollers with locking means is eliminated. When the presses are properly located on the grid, the compressed air supply (which is provided by either the single high volume, low pressure compressor selectively connectible to each of the presses or the self-contained blower in each press) is discontinued. lt should be understood that if a common blower is used each of the movable presses may be provided with a valve or quick-disconnect coupling for individual vent- 7 ing of the chambers as the presses are each located on the grid.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As various changes could be made in the above constructions without departing form the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. Apparatus for fabricating trusses and the like at a work station at which nailing plates are to be driven into opposite sides of abutting wood members; said apparatus comprising a stand at said work station, a carriage mounted on said stand for movement between a retracted position away from the work station and a forward position at the work station, a fluid-operated press having first and second opposed platens and fluid power means for moving said platens toward each other, and means for supporting the press on the carriage in such manner that the press is held against movement relative to the carriage during movement of the carriage between its retracted and forward positions and is floatingly held on the carriage during closing movement of the platens.

2. Apparatus as set forth in claim 1 further comprising second fluid power means for moving said carriage between its retracted and forward positions.

3. Apparatus as set forth in claim 1 further comprising a chamber at the bottom of the stand and means for supplying said chamber with air under pressure to lift the stand slightly and permit easy horizontal movement thereof.

4. Apparatus as set forth in claim 3 wherein the chamber is dome-shaped and the stand is weighted above the chamber.

5. Apparatus as set forth in claim 1 wherein said supporting means comprises an expansible chamber interconnecting said press and carriage.

6. Apparatus as set forth in claim 5 wherein said expansible chamber is a pneumatic actuator.

7. Apparatus as set forth in claim 6 further comprising means for supplying said actuator with air under sufficient pressure to support said press against movement relative to the carriage during movement of the carriage, and means for reducing the pressure in said actuator to floatingly support said press on the carriage during closing movement of the platens.

8. Apparatus as set forth in claim 6 wherein said actuator comprises a housing carried by the carriage, a flexible diaphragm in the housing, and a rod interconnecting the diaphragm and the press.

9. Apparatus as set forth in claim 1 wherein said supporting means comprises means for firmly retaining said press on said carriage during movement of the carriage and spring means for resiliently supporting said press on said carriage during closing movement of said platens.

10. Apparatus as set forth in claim 9 wherein said retaining means comprises a portion of the carriage directly bearing a portion of the weight of said press.

11. Apparatus as set forth in claim 10 further comprising first and second opposed coil compression springs adapted to be compressed together by said first and second platens during closing movement thereof.

12. Apparatus as set forth in claim 11 wherein said first and second springs are coaxial and have substantially equal spring rates for effecting substantially simultaneous movement of said platens at equal rates toward each other.

13. Apparatus as set forth in claim 12 wherein said resilient supporting means is a third coil compression spring coaxial with said first and second springs, and means for vertically moving relative to said carriage the center line upon which said platens close.

14. Apparatus as set forth in claim 1 further comprising spring means resisting closing movement of said platens.

15. A press comprising a fluid cylinder, a first platen carried by said cylinder, a ram working in said cylinder, a second platen opposed to said first platen and carried by said ram, means for supplying fluid pressure tosaid cylinder to move said platens relative to each other, a carriage mounted on a stand for movement between a retracted position and a forward position, and means for supporting said press on said carriage, said means holding said press against movement with respect to said carriage during movement of said carriage between its retracted and forward positions and floatingly with respect to said carriage during movement of said platens.

16. A press as set forth in claim 15 wherein said supporting means comprises a pneumatic actuator.

17. A press as set forth in claim 15 wherein said supporting means comprises means for firmly retaining said press on said carriage during movement of the carriage and spring means for resiliently supporting said press on said carriage during closing movement of said platens, said retaining means comprising a rigid portion of the carriage directly bearing a portion of the weight of said press, said resilient spring supporting means comprising a coil compression spring.

18. Press apparatus comprising a stand, a press having first and second opposed platens, fluid power means for moving said platens in a generally vertical plane toward each other, said fluid power means comprising a cylinder rigid with said first platen and a ram working in said cylinder and carrying said second platen, means for supporting said press on said stand, said means comprising a pneumatic actuator interconnecting said press and stand, means for supplying said actuator with air under pressure for holding said press against downward movement, and means for reducing the pressure in said actuator to permit downwardmovement of said first platen in response to upward movement of said second platen.

19. Apparatus as set forth in claim 18 wherein said pressure reducing means comprises a valve actuated by initial upward movement of said second platen.

20. Apparatus as set forth in claim 19 further comprising a carriage mounting said press on said stand for horizontal movement of said press between a retracted loading and unloading position and a forward operative position.

21. Apparatus as set forth in claim 19 wherein said pneumatic actuator comprises a housing carried by said stand and a diaphragm secured to said press.

22. Apparatus as set forth in claim 21 wherein said housing is carried by said stand by a pair of rods on opposite sides of the press, said rods being secured at their lower ends to said housing and having rocker plates at their upper ends carried by said stand for rocking movement of said press relative to said stand about a generally horizontal axis.

23. Apparatus as set forth in claim 22 further comprising a pair of tubular guides secured to said press and slidably received on said rods.

24. Press apparatus comprising a stand, a press having first and second relatively movable opposed platens, fluid power means for moving said platens toward one another, said fluid power means comprising a cylinder rigid with said first platen and a ram working in said cylinder and carrying said second platen, means for supporting said press on said stand, and resilient means interconnecting said platens, said resilient means comprising first and second opposed coaxial coil springs and means for respectively interconnecting said first and second platens with said first and second springs for compressing said springs toward each other during closing movement of said platens.

25. Apparatus as set forth in claim 24 wherein the first and second springs have equal spring rates and diameters.

26. Apparatus as set forth in claim 25 wherein said supporting means comprising a third coil spring reacting between said stand and the point of abutment between said first and second springs thereby to floatingly support said press relative to said stand.

27. Apparatus as set forth in claim 26 wherein said third spring is coaxial with and of smaller diameter than said first and second springs.

28. Apparatus as set forth in claim 26, which further includes means for vertically moving relative to said stand the center line upon which the platens close.

29. Apparatus as set forth in claim 28 further comprising a tube carrying said third spring at its lower end, said tube having a rocker plate at its upper end carried by said stand for rocking movement of said press on said stand about a generally horizontal axis.

30. Apparatus as set forth in claim 29 wherein said means for interconnecting said platens with said springs comprises a rod slidably received in said tube, said rod being connected at its upper end to said second platen and at its lower end to said second spring, and a sleeve slidable on said tube, said sleeve having an arm secured to said cylinder and carried by said first spring.

31. Apparatus as set forth in claim 29 further comprising a carriage mounting said press on said stand for horizontal movement of said press between a retracted loading and unloading position and a forward operative position.

32. Apparatus for fabricating trusses and the like comprising a plurality of stands, a fluid-operated press carried by each of the stands for driving nailing plates into opposite sides of abutting wood members at the truss joints, each of said presses comprising first and second opposed platens and fluid power means for moving said platens toward each other, and means for facilitating moving and locating at least some of said stands for fabricating various types and sizes of trusses, said latter means each comprising a chamber at the bottom of each of the movable stands and means for 

1. Apparatus for fabricating trusses and the like at a work station at which nailing plates are to be driven into opposite sides of abutting wood members; said apparatus comprising a stand at said work station, a carriage mounted on said stand for movement between a retracted position away from the work station and a forward position at the work station, a fluid-operated press having first and second opposed platens and fluid power means for moving said platens toward each other, and means for supporting the press on the carriage in such manner that the press is held against movement relative to the carriage during movement of the carriage between its retracted and forward positions and is floatingly held on the carriage during closing movement of the platens.
 2. Apparatus as set forth in claim 1 further comprising second fluid power means for moving said carriage between its retracted and forward positions.
 3. Apparatus as set forth in claim 1 further comprising a chamber at the bottom of the stand and means for supplying said chamber with air under pressure to lift the stand slightly and permit easy horizontal movement thereof.
 4. Apparatus as set forth in claim 3 wherein the chamber is dome-shaped and the stand is weighted above the chamber.
 5. Apparatus as set forth in claim 1 wherein said supporting means comprises an expansible chamber interconnecting said press and carriage.
 6. Apparatus as set forth in claim 5 wherein said expansible chamber is A pneumatic actuator.
 7. Apparatus as set forth in claim 6 further comprising means for supplying said actuator with air under sufficient pressure to support said press against movement relative to the carriage during movement of the carriage, and means for reducing the pressure in said actuator to floatingly support said press on the carriage during closing movement of the platens.
 8. Apparatus as set forth in claim 6 wherein said actuator comprises a housing carried by the carriage, a flexible diaphragm in the housing, and a rod interconnecting the diaphragm and the press.
 9. Apparatus as set forth in claim 1 wherein said supporting means comprises means for firmly retaining said press on said carriage during movement of the carriage and spring means for resiliently supporting said press on said carriage during closing movement of said platens.
 10. Apparatus as set forth in claim 9 wherein said retaining means comprises a portion of the carriage directly bearing a portion of the weight of said press.
 11. Apparatus as set forth in claim 10 further comprising first and second opposed coil compression springs adapted to be compressed together by said first and second platens during closing movement thereof.
 12. Apparatus as set forth in claim 11 wherein said first and second springs are coaxial and have substantially equal spring rates for effecting substantially simultaneous movement of said platens at equal rates toward each other.
 13. Apparatus as set forth in claim 12 wherein said resilient supporting means is a third coil compression spring coaxial with said first and second springs, and means for vertically moving relative to said carriage the center line upon which said platens close.
 14. Apparatus as set forth in claim 1 further comprising spring means resisting closing movement of said platens.
 15. A press comprising a fluid cylinder, a first platen carried by said cylinder, a ram working in said cylinder, a second platen opposed to said first platen and carried by said ram, means for supplying fluid pressure to said cylinder to move said platens relative to each other, a carriage mounted on a stand for movement between a retracted position and a forward position, and means for supporting said press on said carriage, said means holding said press against movement with respect to said carriage during movement of said carriage between its retracted and forward positions and floatingly with respect to said carriage during movement of said platens.
 16. A press as set forth in claim 15 wherein said supporting means comprises a pneumatic actuator.
 17. A press as set forth in claim 15 wherein said supporting means comprises means for firmly retaining said press on said carriage during movement of the carriage and spring means for resiliently supporting said press on said carriage during closing movement of said platens, said retaining means comprising a rigid portion of the carriage directly bearing a portion of the weight of said press, said resilient spring supporting means comprising a coil compression spring.
 18. Press apparatus comprising a stand, a press having first and second opposed platens, fluid power means for moving said platens in a generally vertical plane toward each other, said fluid power means comprising a cylinder rigid with said first platen and a ram working in said cylinder and carrying said second platen, means for supporting said press on said stand, said means comprising a pneumatic actuator interconnecting said press and stand, means for supplying said actuator with air under pressure for holding said press against downward movement, and means for reducing the pressure in said actuator to permit downward movement of said first platen in response to upward movement of said second platen.
 19. Apparatus as set forth in claim 18 wherein said pressure reducing means comprises a valve actuated by initial upward movement of said second platen.
 20. Apparatus as set forth in claim 19 further comprising a carRiage mounting said press on said stand for horizontal movement of said press between a retracted loading and unloading position and a forward operative position.
 21. Apparatus as set forth in claim 19 wherein said pneumatic actuator comprises a housing carried by said stand and a diaphragm secured to said press.
 22. Apparatus as set forth in claim 21 wherein said housing is carried by said stand by a pair of rods on opposite sides of the press, said rods being secured at their lower ends to said housing and having rocker plates at their upper ends carried by said stand for rocking movement of said press relative to said stand about a generally horizontal axis.
 23. Apparatus as set forth in claim 22 further comprising a pair of tubular guides secured to said press and slidably received on said rods.
 24. Press apparatus comprising a stand, a press having first and second relatively movable opposed platens, fluid power means for moving said platens toward one another, said fluid power means comprising a cylinder rigid with said first platen and a ram working in said cylinder and carrying said second platen, means for supporting said press on said stand, and resilient means interconnecting said platens, said resilient means comprising first and second opposed coaxial coil springs and means for respectively interconnecting said first and second platens with said first and second springs for compressing said springs toward each other during closing movement of said platens.
 25. Apparatus as set forth in claim 24 wherein the first and second springs have equal spring rates and diameters.
 26. Apparatus as set forth in claim 25 wherein said supporting means comprised a third coil spring reacting between said stand and the point of abutment between said first and second springs thereby to floatingly support said press relative to said stand.
 27. Apparatus as set forth in claim 26 wherein said third spring is coaxial with and of smaller diameter than said first and second springs.
 28. Apparatus as set forth in claim 26, which further includes means for vertically moving relative to said stand the center line upon which the platens close.
 29. Apparatus as set forth in claim 28 further comprising a tube carrying said third spring at its lower end, said tube having a rocker plate at its upper end carried by said stand for rocking movement of said press on said stand about a generally horizontal axis.
 30. Apparatus as set forth in claim 29 wherein said means for interconnecting said platens with said springs comprises a rod slidably received in said tube, said rod being connected at its upper end to said second platen and at its lower end to said second spring, and a sleeve slidable on said tube, said sleeve having an arm secured to said cylinder and carried by said first spring.
 31. Apparatus as set forth in claim 29 further comprising a carriage mounting said press on said stand for horizontal movement of said press between a retracted loading and unloading position and a forward operative position.
 32. Apparatus for fabricating trusses and the like comprising a plurality of stands, a fluid-operated press carried by each of the stands for driving nailing plates into opposite sides of abutting wood members at the truss joints, each of said presses comprising first and second opposed platens and fluid power means for moving said platens toward each other, and means for facilitating moving and locating at least some of said stands for fabricating various types and sizes of trusses, said latter means each comprising a chamber at the bottom of each of the movable stands and means for supplying said chambers with a relatively large volume of air under relatively low pressure to lift said movable stands for easy horizontal movement thereof, the lower portion of the chamber having an opening substantially the size of the bottom of the stand.
 33. Apparatus as set forth in claim 32 further comprising a locating grid on a base on which said stands rest.
 34. Apparatus as set forth in claim 32 further comprising suction cups in said chambers and means for drawing a vacuum in said suction cups for holding said stands against movement during the pressing operation.
 35. Apparatus as set forth in claim 32 wherein said chambers are dome-shaped and said stands are weighted above said chambers.
 36. In a roof truss forming machine for assembling and nailing with nail plates timbers into a planar roof truss, the improvement comprising, a stand having support means for supporting the timbers in position where they are to be nailed, a cradle movably supported on the stand and laterally movable toward and away from the timbers supported by the support means of the stand, and a hydraulically operated C-clamp including a piston and a cylinder, a platen secured to the piston and vertically movably guided by the cradle and normally resting by gravity on the cradle below the plane of the timbers supported by the stand, and a C-clamp member secured to the cylinder below the platen and having a pressure plate above the plane of the timbers supported by the stand, the arrangement being such that when the cradle is moved toward the timbers supported by the support means of the stand with the platen and pressure plate of the hydraulically operated C-clamp in vertical alignment with the timbers where they are to be nailed, the application of hydraulic pressure to the cylinder and piston causes the platen to rise and the pressure plate to lower for simultaneously pressing nail plates into opposite sides of the timbers. 